Rotating data storage media having multiple recording layers is one method which is employed to increase the amount of data that can be stored in a given volume. As used herein, the term “layer” refers broadly to the recording surfaces of a stack of disk platters secured to a single spindle as well as to recording layers embedded within a single piece of media. FIG. 1 is an example of the former, a hard disk stack 100 with four platters 110, 120, 130, 140. Each platter 110, 120 has two recording surfaces, 110A and 110B, 120A and 120B, 130A and 130B, and 140A and 140B, respectively. As is known, the platters are secured to a spindle 150 and rotate together. FIG. 2 is an example of the latter, a cross-section of a multi-layer optical disc 200 having four recordable layers 210A, 210B, 210C, 210D embedded therein between spacer layers. Multi-layer optical disk 200 may be a DVD (Digital Versatile Disk), HD-DVD (High Definition DVD) disk, or a Blu-Ray disk. The layers are accessed optically via laser 220. Data is typically initially recorded in sequential blocks, continuing from one layer to the next. In a re-writable environment, as data is modified or overwritten, blocks with new data may become more spread out to fill gaps left by old, erased or moved data.
While increasing data density by recording to multi-layer media provides many benefits, some data may be at risk if part or all of a layer becomes unreadable, such as from a scratch, media defect, head crash or aging, among others. Consequently, a need remains for improving the reliability of multi-layer media and, therefore, the security of the data recorded thereon.